1. Field of the Invention
The present invention relates to an adsorptive ethanol drying apparatus using microwaves and an operating method thereof, and more particularly to an adsorptive ethanol drying apparatus in which microwaves are applied during the regeneration of an absorbent conducted in a continuous adsorption process for drying ethanol, so that the absorbent regeneration can be rapidly achieved at a temperature lower than that used in a conventional heating type regeneration method and within a reduced processing time, thereby being capable of allowing an efficient use of energy while improving the productivity per adsorbent mass. The present invention also relates to a method for operating this adsorptive ethanol drying apparatus.
2. Description of the Related Art
An azeotrope of water and ethanol (92-95% ethanol) can not be separated into water and ethanol using normal distillation process. Since water molecules in this azeotropic mixture are selectively adsorbed on zeolite 3A or 4A, these molecular sieves are conventionally used in ethanol drying. When the ethanol azeotropic mixture is passed through the adsorption tower, water molecules are adsorbed to the adsorbent, so that ethanol of a high purity (95.5 wt %) is produced. Once the adsorbent is saturated with water, it should be dehydrated for a subsequent re-use thereof. For a dehydration of the adsorbent, a heating type description process has been conventionally used. The heating type desorption process involves heating the adsorbent to about 300xc2x0 C. or more.
Generally, molecules having dipolar moment, such as water molecules, are easily heated or exhibits an increased mobility when they are irradiated by microwaves. Where microwaves are applied to the regeneration of an adsorbent adsorbed with polar molecules, the energy of the microwaves is consumed to directly heat the adsorbate or to increase the mobility of the adsorbate without being consumed to heat the adsorbent because the adsorbent is less sensitive to the microwaves. In this case, accordingly, the regeneration of the adsorbent can be achieved at a temperature lower than that of a heating type desorption process, for example, at a temperature of about 200xc2x0 C.
Various techniques associated with an adsorptive ethanol dehydrating process or apparatus have been known. For example, there is a method in which had adsorption heat generated in accordance with an adsorption of molecules is efficiently used at a subsequent adsorption step (U.S. Pat. No. 4,373,935), a method in which ethanol produced is supplied in a heated state in a desorption process (U.S. Pat. No. 4,407,662), a method in which carbon dioxide of a high pressure is supplied in a desorption process (U.S. Pat. No. 4,273,621), and a method in which heated ethanol vapor is supplied along with carbon dioxide in a desorption process. However, these techniques are different from the present invention in that they do not apply microwaves during a desorption process.
The present invention is adapted to apply microwaves in a desorption process for regenerating an adsorbent adsorbed with polar molecules such as water, thereby allowing the desorption process to be conducted at a low temperature, as compared to a conventional heating type desorption process, so that it is possible to improve the productivity per adsorbent mass.
The present invention relates to an adsorbent regeneration method wherein microwaves are applied in a continuous adsorption process in which substances sensitive to microwaves are adsorbed to an adsorbent. Conventionally, an adsorbent strongly adsorbed with substances is regenerated by directly heating it to a high temperature or using a heated material such as hot steam or gas. In accordance with the present invention, microwaves are irradiated to the adsorbate in order to desorb the adsorbate from the adsorbent.
When microwaves are irradiated to polar molecules such as water, the mobility of those molecules is increased as the arrangement of the molecules is continuously changed. At this time, an increase in temperature also occurs due to frictional heat generated among the molecules. By virtue of the increased mobility of molecules and the increased temperature resulting from an application of microwaves, the molecules adsorbed to the adsorbent can be easily desorbed from the adsorbent, so that the adsorbent is regenerated.
Therefore, an object of the invention is to provide an adsorptive ethanol drying apparatus using microwaves and an operating method thereof, in which microwaves are applied in an adsorbent regeneration process, so that the ethanol regeneration process is conducted at a relatively low temperatures, as compared to conventional adsorptive ethanol drying processes.
Another object of the invention is to provide an adsorptive ethanol drying apparatus using microwaves and an operating method thereof, which are capable of achieving a desorption of substances adsorbed to the adsorbent without any requirement to cool the adsorbent or while involving a cooling process for a reduced time, thereby improving the productivity per adsorbent mass.
In accordance with one aspect, the present invention provides an adsorptive ethanol drying apparatus for vaporizing ethanol supplied from an ethanol storage tank, and adsorbing water contained in the vaporized ethanol to an adsorbent charged in adsorption towers while condensing ethanol of a high purity, free of the water, in a separate storage tank, comprising: a microwave generating device for generating microwaves; a first waveguide connected to the microwave generating device; a switching waveguide connected to the microwave generating device via the first waveguide and pneumatic driven to switch the microwaves between the adsorption towers; a second waveguide arranged around each of the adsorption towers and connected to the switching waveguide, the second waveguide serving to guide the microwaves transmitted from the switching waveguide to the adsorption tower; and a vacuum pump adapted to apply vacuum to the adsorption towers for an easy desorption of adsorbates adsorbed to the adsorbent in the adsorption towers; whereby the adsorbates adsorbed to the adsorbent in the adsorption towers are desorbed by the waveguides guided to the adsorption towers in an alternating fashion by the switching waveguide and the vacuum generated by the vacuum pump.
In accordance with another aspect, the present invention provides an adsorptive ethanol drying method for forcing a vaporized ethanol azeotropic mixture to pass through adsorption towers to adsorb water contained in the vaporized ethanol azeotropic mixture to an adsorbent charged in each of the adsorption towers while condensing ethanol in a storage tank, comprising the steps of: simultaneously with the adsorption step conducted in one of the adsorption towers, guiding microwaves generated from a microwave generating device to the other adsorption tower via waveguides in accordance with a switching operation of a switching waveguide, thereby activating water adsorbed to the adsorbent in the adsorption step to allow the water to be desorbed from the adsorbent; and applying slight vacuum to the other adsorption tower, thereby removing the desorbed water.